1. Field of the Invention:
The present invention relates to apparatus for applying a viscous substance for use, for example, in applying frit to the sealing part of a funnel in manufacturing a cathode-ray tube and, more specifically, to a nozzle for such an apparatus.
2. Description of the Prior Art:
Nozzles for a conventional viscous substance applying apparatus for use, for example, in applying frit to the sealing part of the funnel of a cathode-ray tube are shown in FIGS. 4 and 5.
The nozzle 1 of FIG. 4 is provided with a valve element 4 which opens or shuts only the frit inlet 3 of a frit chamber 2. The valve element 4 is controlled for opening or closing the frit inlet 3 by pneumatically raising or lowering a piston 6 fitted in a cylinder 5 and connected to the valve element 4.
The nozzle 1 of FIG. 5 is provided with a valve element 8 which opens or shuts only the frit outlet 7 of a frit chamber 2. In FIGS. 4 and 5, indicated at 9 and 10 are air inlet-outlet ports, and at II is a frit inlet port.
After applying the frit to the sealing part of the funnel, a fluorescent screen and a metal backing are formed, then the funnel is joined to a panel mounted with a color selection electrode, then an electron gun is attached to the funnel, and then the funnel is evacuated to complete a cathode-ray tube.
In applying the frit with the nozzle 1 of FIG. 4, the valve element 4 is moved downward to open the frit inlet 3 at the start of discharging the frit; consequently, a portion of the frit remaining in the frit chamber 2 is pushed out from the nozzle 1 by the downward movement of the valve element 4, so that the frit is unavoidably applied to the sealing part of a funnel in a width greater than the desired predetermined width. At the end of discharging the frit, the valve element 4 is moved upward to close the frit inlet 3. Therefore, the frit is sucked back into the frit chamber 2, and hence the width of the frit applied to the sealing part of the funnel does not change. FIG. 6 illustrates a mode of spread of the frit 13 applied to the sealing part 12 with the nozzle 1 of FIG. 4. Since an excessive amount of the frit is discharged at the start of applying the frit, the frit spreads in a width wider than the predetermined width at the frit application starting position 14. The spread of the frit 13 at the frit application ending position 15 is normal.
In applying the frit with the nozzle 1 of FIG. 5, the valve element 8 is moved upward to open the frit outlet 7 at the start of discharging the frit 13, and hence the frit 13 is applied in an appropriate width at the frit application starting position 16 as illustrated in FIG. 7. However, since the valve element 8 is moved downward at the end of discharging the frit to close the frit outlet 7, a portion of the frit 13 remaining in the frit chamber 2 is discharged excessively, and hence the frit 13 spreads in a width greater than the predetermined width at the frit application ending position 17 as illustrated in FIG. 7.
Thus, it is difficult to control the width of spread of the frit correctly at the start or at the end of frit application when such conventional nozzles are used. Particularly, when the manufacturing condition requires overlapping the frit application starting position and the frit application ending position, the width of the overlapping part necessarily becomes greater than the predetermined width.